Characterizing Stormwater Basin Conditions Using Tracked BMP Inspection and Rating Reports from the Virginia Department of Transportation

Abstract

Studies have rarely used stormwater best management practice (BMP) condition rating data to quantify changes in condition ratings and characterize condition issues, making it challenging to implement proactive maintenance practices. To help address this knowledge gap, we answer the following questions pertaining to a widely used stormwater BMP: detention and retention basins. (1) How often do basin condition ratings change over time? (2) What are specific site and structural condition issues identified during condition inspections? (3) What issues and site characteristics correspond with basins that experience a rapid decline in condition rating, meaning a decrease in two or more condition rating levels within a single year? We do this by characterizing basin condition ratings and associated issues using information included in more than 5,500 basin inspection reports, each containing more than 200 questions, stored in the Virginia Department of Transportation (VDOT) asset management system. On average, between 5.6 and 8.3 issues were recorded per visit for D-rated and E-rated basins compared with 0.03 to 1.8 issues for A-rated and B-rated basins. Of the 901 basins with three consecutive years of inspections, 41% and 35% had condition ratings that changed from 2020 to 2021 and from 2021 to 2022, respectively. The most common issues associated with rapid condition rating decline included major corrosion on the low flow orifice trash/debris rack, control structure, and pipe. Rapidly declining condition ratings were observed in 67% of VDOT’s nine independent management districts, suggesting rapid declines occur independently of management practices. Higher median elevation and percent slope attributes and lower median population were correlated with basins experiencing rapid condition rating decline. Using these results as context, we discuss considerations for improving BMP inspection data quality and opportunities for supporting proactive BMP management practices that can benefit other agencies managing a large portfolio of stormwater assets. Stormwater asset management systems can be leveraged to track changes in the conditions of best management practices by collecting, storing, and processing detailed asset inspection reports. This study showed that detention/retention basin condition ratings can change within a single year’s time and that rapidly declining condition ratings, meaning ratings that decline by two or more levels within a single year, can occur independently of management practices. Inspector certification, automatic system-issued ratings, inspection report auditing, and controlled vocabulary during data entry of inspection reports should be considered to reduce bias and improve the quality of condition rating data in support of proactive maintenance.